Cylinder Head Cracks: Symptoms & Repair Cost

By Dan Collins

Published 15:44 pm

Engines. If you love your car you’ve got to love its engine too, because without it your vehicle is going nowhere at all. Inside that engine you will find a whole host individual parts and components all working together in perfect harmony so that when you press the gas pedal, the vehicle will move.

That’s all well and good, provided that all the parts and components are happy and working together. When they start to fail though you can see this in reduced engine performance and perhaps even a complete breakdown.

No one wants that, so in this article we’re going to take a look at one of the more vulnerable parts of the engine, the plucky little cylinder heads. We’ll look at the symptoms you’ll notice if your own cylinder heads are cracked, and then we’ll evaluate the cost you’ll likely face to repair them.

But first:

What is a Cylinder Head?

The Cylinder Head is a key component within an internal combustion engine. So if you drive an electric vehicle – congratulations, you have no cylinder heads to crack.

For most of us driving around in traditional gas powered cars however, we are relying on Cylinder Heads to help power our vehicles. So what are they?

Well, within the engine block of an internal combustion engine there are cylinders. It is within these cylinders that gas and air mix and are sparked into combustion. This combustion forces the drive chain of the vehicle to move (via pistons) which in turn transfer energy to the driving wheels of the car.

The short version of that? Small controlled explosions in tubes move the vehicle forwards (or backwards).

How cool is that?

What About the Cylinder Heads?

We’re getting there, jeez.

The cylinder heads are located, as their name suggests, at the top of the cylinder. The heads close the cylinder and contain the gas and air mixture plus the combustion effect. They then open to vent the exhaust gases.

They do this thousands of times per minute, and each time they close they create a pressure seal within the cylinder. Each time they open they are enveloped in hot gases.

That is a pretty tough life, which is why Cylinder Heads are made of tough materials. On older cars they are often made of iron for example, whilst modern cars will opt for aluminum as the material of choice.

So What’s The Problem?

The problem is that whilst they are made of tough metal, they also have to be pretty lightweight. If the cylinder was too heavy, it would not be able to complete its arc of movement within the cylinder quickly enough. That would mean that the engine would less be efficient.

For vehicle manufacturers then it is a careful balancing act. On the one hand the Cylinder Head must be tough enough to last through years of service – no one wants to be stripping and replacing their Heads every six months.

On the other it must be lightweight enough to perform it’s function without affecting engine performance.

Sounds Like a Tough Gig

It is, but vehicle manufacturers have pretty much got the formula down by now. Generally speaking an aluminum cylinder head is going to give you around five years of useful life. An iron one can sometimes last a little longer, say six or even seven years.

After that time span, every cylinder head is going to be in danger of cracking. Luckily, there are a number of symptoms that you can look for that indicate a cracked cylinder head.

Symptoms to keep an eye out for include:

Symptoms of a Cracked Cylinder Head

1. Time

Not strictly a symptom but certainly something to bear in mind. If your vehicle is brand new to up to about two or three years old, then any issues with the engine are unlikely to be related to a cracked cylinder head. Please note that we said unlikely, not impossible!

2. Leaking Oil

The Cylinder Head contains oil. This serves to both lubricate its movement and also to assist with dissipating heat. Both very useful functions, so thank you oil! As maybe expected when something cracks though, a cracked Cylinder Head is going to start leaking that oil pretty quickly.

There is a couple of way this symptom could present itself. First you may notice a patch of oil that has pooled underneath the engine when you have the vehicle parked in a position for a period of time.

Secondly, on a modern car at least, you may get the good old “Check Oil” engine light pop up on the dashboard display.

3. Coolant Leak

Liquid coolant is also deployed in and around the area of the engine blocks that contains the Cylinder Heads. Liquid coolant serves the purpose of, well, helping to keep things cool, including the Heads themselves. So again, when they crack this can lead to coolant leak.

Just as with the oil leaks this can present itself in a couple of different ways. So on the one hand you may get a visual clue. This could be an obvious sign of coolant liquid leaking out mixed in with leaking oil – it could also be coolant leaking by itself.

You are also going to get a warning light pinging into life on the dash display. This one will be the “Check Engine Temperature” light. This is because when the Cylinder Heads are leaking coolant, you will naturally have less coolant in the engine to, well, keep it cool.

4. Poor Performance

We’re just talking about the engine here; so don’t go running out to get any of the little blue pills. As we described above, the Cylinder Heads play a big part in the running of an internal combustion engine.

That means when the Heads are cracked, they will affect engine performance. Specifically, they will not be able to form the complete seal that is required for efficient combustion. Instead, compressed air will be allowed to leak out meaning that each combustion stroke in the engine is weaker than it should be.

That in turn is going to translate into weak engine performance. You will likely notice this the most when you place performance pressures on the vehicle. For example the vehicle may struggle when driving up an incline or it may be sluggish when pulling away from a standing start, such as when a red light changes to green.

5. Misfiring Engine

This also relates somewhat to the point above. Again, as we described above, the Cylinder Head closes the cylinder to create the pressurized atmosphere into which the gas and air mixture is injected and ignited to cause combustion.

If the Cylinder Head is cracked the cylinder won’t be held at the right pressure, which means that the mixture of gas and air will not be correct. This can lead to poor combustion, which affects performance (as described above).

In severe cases it can also lead to that combustion not happening at all! In that case, the engine will misfire. This is of course going to have a severe impact on engine performance.

It is also going to have a bad effect on the engine as a whole however. A misfired cylinder will see the contents of that cylinder being forced through the entire engine system. Fuel that has not been burnt properly in the cylinders can damage and gum up components further down the engine system.

For this reason, misfires are one of the more serious symptoms of a cracked Cylinder Head and should be investigated – and repaired – promptly.

6. Smoking Engine

Last but not least, and we have saved the best (or rather worst) for last. When a Cylinder Head is extremely damaged, it may start to vent exhaust gases directly into the engine space. This will present to you, the driver, as smoke leaking out from under the hood.

A Cylinder head in this condition is really on it’s last legs and must be replaced as soon as possible – in reality, that really means that it needs to be replaced pretty much immediately.

We would strongly recommend that you don’t let your Cylinder Heads get to the point they are displaying this symptom. Instead, keep an eye out for the four symptoms above, and replace your heads before they get to the stage of spewing smoke everywhere!

The Cost of Repairing a Cracked Cylinder Head

Those are the symptoms of a cracked Cylinder Head. Now you know what to look out for, naturally if you notice any of them you are likely – or at least recommended – to take your vehicle to a pro mechanic for a service.

If the issues does turn out to be a cracked Cylinder Head, then you may be wondering what the financial damage will be.

Replacing a cracked Cylinder Head is not a very demanding job for a well-equipped mechanics shop. An average price to replace an aluminum Cylinder Head, including parts and labor, will be in the region of $500.

Replacing an iron Cylinder Head can be a little more expensive, mainly because these parts are harder to source. With an iron cylinder head, the replacement parts alone can be billed out for $500 by themselves. Add in labor charges and replacing an iron Cylinder Head can end up costing from about $800 up to $1,000.

Conclusion

So there you have it, you know what to look out for and a ball park estimate of how much it will cost to fix a cracked Cylinder Head.